Aramids, particularly those that can be cast as films or spun into fibers, can show poor stability, as measured for retention of tenacity, when exposed to conditions favoring hydrolysis, for example, aqueous alkaline conditions. This may result in diminished performance, particularly during certain industrial uses of these polymers. It would be desirable to enhance the tenacity retention of aramids while, at the same time, maintaining other useful properties typically associated with aramids, such as their excellent performance characteristics under high-temperature.
Relatively high levels of alkoxy substitution has been used to increase the meltability of aramids which, however, has caused deterioration of characteristic aramid properties. See, for example, Ballauf et al., J. Polymer Sci. Part A. Polymer Chem., 31, p. 1609-19 (1993). An increase in aramid solubility in comparable, highly substituted aramids is described by Clauss et al., Macromolecules, 25, p. 5208-14 (1992). The use of highly substituted aramids in films is described by Damman et al., Polymers for Adv. Technologies, 5, p. 615-17 (1994).
The present applicant has found that the incorporation of relatively low levels of alkoxy and/or alkyl substitution along the chain of an aramid copolymer, as dislosed herein, can surprisingly improve the hydrolytic stability of the copolymer, but does not adversely affect the excellent high-temperature and other properties typically associated with aramids. Following synthesis of the novel copolymers herein described, the copolymers may be subsequently subjected to heat treatment under tension as part of a commercial process.